Leviathans are gigantic "living-meteors". Their sole purpose is to spread Phazon from the celestial body known as Phaaze once every century, to corrupt planets across the universe in order to create more Phazon-based planets, similar to Phaaze. The core of the Leviathan is very strong and can only be destroyed by a stream of Phazon or a powerful laser blast. These creatures were notable not only for their ability to create and spread Phazon, but also because of their most powerful ability: generating Wormholes to allow them to travel anywhere throughout space.
There have been five recorded cases of Leviathan impact.
- Tallon IV's Leviathan
- Aether's Leviathan
- Bryyo's Leviathan
- Elysia's Leviathan
- Pirate Homeworld's Leviathan
Leviathans are the "children" of Phaaze. Born in a serpentine womb deep within the planet, they feed on vast amounts of Phazon energy until they develop a Phazon Core, which marks their transition into adolescence.
Before this, they are extremely unstable, though naturally extremely resistant, and cause massive explosions if damaged before full maturity. Once they reach adolescence, the Leviathans are slowly pushed upward to the surface until they mature to their adult size. The oldest Leviathans are up closest to the surface while the youngest are below. As Leviathans are launched into space, the younger ones move closer and closer to the surface. As mentioned above, an unspecified number of these creatures are launched every 100 years; the reason behind this century-long wait is likely the required time for infants to reach full maturity. Finally, once Phaaze has found a planet to corrupt, it launches the Leviathan into space, in hopes of impacting a planet.
Leviathans are a silicon/Phazon-based bioform in that, at full maturity, appear to be made of a rocky substance (perhaps a form of Phazite) which is likely why information pertaining to them refers to them as meteors. They are covered with large patches of Phazon and have long tentacles growing out of their sides. The inside of a Leviathan appears similar to a cave containing various Phazon-based life and Phazon-generating organs. The passages that lead to the core chamber of the Leviathan appear as transparent tubes, similar to veins, but without liquid within them. There are doors in the Leviathan that seem to be a type of sphincter valve with a weak energy field covering it. The core chamber is a large spherical room, with many pulsating and moving objects which may be organs. The Phazon Core itself resides at the top of the chamber in a sealed sac-like sheath. The Core's appearance is that of a large, round, insectoid creature connected to the ceiling by several cords that it moves around with. It is covered in Phazon growths, has several eyes and a mandible-like mouth. The chamber is also usually where the Leviathan's guardian resides. Because the Leviathans on Tallon IV and Aether were not expressly shown, it is difficult to say which attributes of the three featured in Corruption are characteristics of immature Leviathans and which ones apply to all.
After ejecting from Phaaze, the Leviathan will create a wormhole to shorten its journey to the intended planet. The Leviathan will home onto its closest target and impact the planet, spreading Phazon from the collision. The strength of this collision has been known to vary greatly, sometimes leaving huge scars upon the surface of the impacted planet. After collision, the Leviathan's Phazon Core, which it developed at the end of its infant stage, slowly seeps its way into the planet, spreading corruption and replacing the ecosystem with one that is Phazon-based. At this point, the Leviathan may possibly attract a native creature and corrupt it with massive amounts of Phazon. The corrupted creature serves as the Leviathan's guardian, to protect its Phazon Core. Some time after this, the Leviathan itself will die, leaving behind the "husk" of its body which will serve as armor to protect the core's environment against attacks from the outside.
Controlled by Dark Samus
Once Dark Samus returned to Phaaze, with the help of the stolen Aurora Unit 313, she was able to control when and where a Leviathan would launch and land by fusing them with the stolen technology. This allowed her to spread Phazon throughout the universe far more effectively and strategically. She used this ability to launch four Leviathans: one to the Pirate Homeworld (to corrupt the resident Pirate forces and thus secure a powerful army), one to Bryyo (to seize control of the planet's priceless Fuel Gel and cut off the Federation's supply of it), another to Elysia (a Federation spy base, originally built by the Chozo), and the fourth to Norion (one of the Federation's greatest naval strongholds).
The Leviathan that was aimed for Norion was destroyed before impact, thanks to the efforts of Samus Aran and other Bounty Hunters. The other three Leviathans survived and were able to pour great amounts of Phazon into each planet. The ones in Bryyo and Elysia were protected by great energy shields, while the Space Pirate Homeworld one was so heavily defended that only one cargo route was allowed to reach the Leviathan itself. In orbit around the Pirate Homeworld, the Space Pirates had outfitted a fifth Leviathan with weapons; however, with Samus's help, the Federation took control of it, using its wormhole-generating abilities to warp to Phaaze.